Using membrane multilayers and esr spectroscopy, the orienation of various membrane-bound paramagnetic molecules is being studied. The molecules to be investigated are the various electron transport components of the bacterium Rhodospirillum rubrum. Also under investigation will be a membrane-bound Mn 2 ion signal detected in chloroplasts. We will attempt to determine any association between this signal and the oxygen-evolving system. Finally, the possibility of detecting membrane-bound nitrogenase will be studied.